We reported last month that SecondMarket and AngelList had hatched a plan to let accredited investors make small-dollar investments — as low as $1,000 — in Silicon Valley technology startups. Today, we learned that the experiment has been declared a success, and this partnership will continue with a new batch of hot startups.

It must be frustrating to be an early Twitter employee. All around Silicon Valley, companies in the social networking space are going public, minting hordes of new millionaires and billionaires. But with little revenue of its own, Twitter is hoping to stay private.

SecondMarket, a company that lets people buy shares in private companies — including in popular pre-IPO companies like Facebook, Twitter, and Groupon — said it has raised $15 million in a third round of financing.